Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Common star collimation mistake

This topic has been archived. This means that you cannot reply to this topic.
239 replies to this topic

#76 Jason D

Jason D

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 7397
  • Joined: 21 Oct 2006

Posted 07 March 2015 - 10:01 AM

Last night I tried the star collimation technique outlined by Mike Lockwood in his website http://www.loptics.c.../starshape.html

The technique is not easy. It took me a while to make "mental" adjustments to use it. Below are the initial issues I ran into:

1- When I defocused to observe the direction of the "bulge/pull" of the expanding star at high magnification, the scope vibrated and I could not detect the expansion direction with good certainty. The little vibration was caused by touching/twisting the focuser knob. The vibration amount is small but it was enough to impact readability.

2- I initially was expanding the defocused star too much. The offset of the secondary shadow was throwing me off.

3- In general, the mental power of suggestion was strong. When I mentally suggested that the bulge is moving to the right, I saw it it moving to the right. In the second attempt, I mentally suggested that the expansion was in the opposite direction and I saw it as such.

 

The reason I listed the above issues is to convey that Mike's technique will require practice and more practice to master it. After spending around an hour practicing and making steps/mental corrections, I was able to get a good handle on the technique. Here is what I eventually was doing:

 

1- I started off with a well-collimated scope then placed my paracorr

2- I severely miscollimated the primary mirror using only two knobs

3- I placed a low magnification eyepiece to locate Procyon

4- Using the low magnification eyepiece, I defocused the star outward too much then used only two primary knobs to recenter the dounut shape in the defocused star. This is meant as a coarse collimation to bring collimation closer. Only one of the two knobs was used in the initial miscollimation. The idea is to enforce fairness during re-collimation. 

5- I replaced the low magnification eyepiece with highest-powered eyepiece. I took magnification up to 660X. I have an equatorial table. Tracking was not a problem.

6- I used the expansion star technique described by Mike in his website. Few hints:

   a) Use the highest magnification eyepiece you have. The technique works better at high magnification. In my case, I used my 2-4mm TV eyepiece set at 2mm.

   b) Do not defocus too much 

   c) Practice to mentally subtract/cancel vibrations. It can be done. I did it. You will need to expand/reset repeatedly while mentally canceling vibrations.

   d) Defocus on both direction as Mike mentioned

   e) One thing helped me is concentrating on the expansion in the Y direction then again on in the X direction while I repeatedly expanded/reset. Once I got a feel for X and Y amounts, I moved the star in the expansion direction referencing the X/Y relative amounts.

   f) Resist looking at the Fresnel rings. Just concentrate on the bulge/pull/expansion direction.

 

I repeated the above 6 time. Below are the results:

 

star_collimation_15.jpg

 

I am pleased with the results. Much better than using the traditional star collimation technique. I guess you could say that Mike Lockwood rewrote the book on star collimation :)

By no means I have mastered Mike's technique. I need more practice and experience.

 

Jason



#77 Jason D

Jason D

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 7397
  • Joined: 21 Oct 2006

Posted 07 March 2015 - 10:08 AM

 

I would pre-qualify Nils Olof statement with the following : Anyone who is planning to re-spot his/her primary mirror using star collimation should first prove to himself/herself that they can achieve highly consistent results.
 
Jason


I don't have the equipment to try, but I would believe the technique of planetary photographers might work to beat the seeing: take a lot of short exposures of a star (focused), with Airy disk and rings. Select a small subset of images with the least broken-up rings, add them and check the symmetry of the rings (innermost at least). An asymmetric intensity ought to reveal even small amounts of coma.

I believe Vic and others who have tried many mirrors, have not found visual signs of miscollimation after instrument collimation using a well centered spot. But what about "homemade" mirrors, maybe with less than perfectly circular blanks?

Nils Olof

 

 

I do not know how well astrophotography technique will perform. If it provides highly consistent results over few nights, then the owner can feel comfortable that he/she has located the optical center.



#78 Kipper-Feet

Kipper-Feet

    Viking 1

  • *****
  • Posts: 680
  • Joined: 22 Jan 2014

Posted 07 March 2015 - 10:47 AM

"Perfect collimation" is a pipe dream, but e.g. to judge the acceptable deviation as seen in Jason's images, you may set the tolerances to perhaps 1/2 or 1/3 of the tabulated radii (1/4 to 1/6 of the diameters).

 

Nils Olof, since your Table is tabulated for F/ratio and the corresponding diameter D, I have to do the following to make sure that I know why it is that you are now speaking about tabulated radii.  

 

I understand that your Table refers to the diameter D of the sweet-spot at the level of the focal plane.

 

You suggest that it would be 'safer' to use a 'smaller' spot in which the coma would be 'lower'.

 

The reduced diameter of this 'smaller' spot could be made to be either D/2 or D/3.

 

The radii of these 'smaller' spots would then be D/4 or D/6 respectfully.

 

These 'smaller' spots, and their respective D/4 and D/6 radii, are in the focal plane.

 

Since our Cheshire tools magnify these radii by 2x in their reads at the level of the primary mirror, we can set the tolerances, as seen in the Cheshire photos, as being double those i.e. 2 x D/4 = D/2 or 2 x D/6 = D/3 respectively.

 

This is, then, where Jason gets his tolerance D/2.  Right?

 

So, another worked example, with my f/6 scope: 

 

Diameter of relatively coma-free spot as per your Table = D = 4.8mm

 

Smaller sweet-spot #1

 

Diameter of a smaller, mostly coma-free spot = D/2 = 4.8mm ÷ 2 = 2.4mm

 

Radius of this smaller, mostly coma-free spot = D/4 = 4.8mm ÷ 4 = 1.2mm at the level of the focal plane.

 

Tolerance for PAE as seen in the Cheshire photos = 2 x 1.2mm = 2.4mm.

 

I recognize that this 2.4mm tolerance equates to D/2.

 

Much smaller sweet-spot #2

 

Diameter of a much smaller, mostly coma-free spot = D/3 = 4.8mm ÷ 3 = 1.6mm

 

Radius of this much smaller, mostly coma-free spot = D/6 = 4.8mm ÷ 6 = 0.8mm at the level of the focal plane.

 

Tolerance of PAE as seen in the Cheshire photos = 2 x 0.8mm = 1.6mm

 

I recognize that this 1.6mm tolerance equates to D/3.


Edited by Richard Roseweir, 07 March 2015 - 10:49 AM.


#79 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 43270
  • Joined: 23 Jun 2003

Posted 07 March 2015 - 11:05 AM

Last night I tried the star collimation technique outlined by Mike Lockwood in his website http://www.loptics.c.../starshape.html

The technique is not easy. It took me a while to make "mental" adjustments to use it. Below are the initial issues I ran into:

1- When I defocused to observe the direction of the "bulge/pull" of the expanding star at high magnification, the scope vibrated and I could not detect the expansion direction with good certainty. The little vibration was caused by touching/twisting the focuser knob. The vibration amount is small but it was enough to impact readability.

2- I initially was expanding the defocused star too much. The offset of the secondary shadow was throwing me off.

3- In general, the mental power of suggestion was strong. When I mentally suggested that the bulge is moving to the right, I saw it it moving to the right. In the second attempt, I mentally suggested that the expansion was in the opposite direction and I saw it as such.

 

The reason I listed the above issues is to convey that Mike's technique will require practice and more practice to master it. After spending around an hour practicing and making steps/mental corrections, I was able to get a good handle on the technique. Here is what I eventually was doing:

 

1- I started off with a well-collimated scope then placed my paracorr

2- I severely miscollimated the primary mirror using only two knobs

3- I placed a low magnification eyepiece to locate Procyon

4- Using the low magnification eyepiece, I defocused the star outward too much then used only two primary knobs to recenter the dounut shape in the defocused star. This is meant as a coarse collimation to bring collimation closer. Only one of the two knobs was used in the initial miscollimation. The idea is to enforce fairness during re-collimation. 

5- I replaced the low magnification eyepiece with highest-powered eyepiece. I took magnification up to 660X. I have an equatorial table. Tracking was not a problem.

6- I used the expansion star technique described by Mike in his website. Few hints:

   a) Use the highest magnification eyepiece you have. The technique works better at high magnification. In my case, I used my 2-4mm TV eyepiece set at 2mm.

   b) Do not defocus too much 

   c) Practice to mentally subtract/cancel vibrations. It can be done. I did it. You will need to expand/reset repeatedly while mentally canceling vibrations.

   d) Defocus on both direction as Mike mentioned

   e) One thing helped me is concentrating on the expansion in the Y direction then again on in the X direction while I repeatedly expanded/reset. Once I got a feel for X and Y amounts, I moved the star in the expansion direction referencing the X/Y relative amounts.

   f) Resist looking at the Fresnel rings. Just concentrate on the bulge/pull/expansion direction.

 

I repeated the above 6 time. Below are the results:

 

attachicon.gifstar_collimation_15.jpg

 

I am pleased with the results. Much better than using the traditional star collimation technique. I guess you could say that Mike Lockwood rewrote the book on star collimation :)

By no means I have mastered Mike's technique. I need more practice and experience.

 

Jason

But if you used your tool, would you have settled for ANY of those results?



#80 Jason D

Jason D

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 7397
  • Joined: 21 Oct 2006

Posted 07 March 2015 - 11:34 AM

 

But if you used your tool, would you have settled for ANY of those results?

 

 

 I am a strong believer in quality collimation tools. 

 

1- If collimation tools deliver highly consistent results

2- And if star collimation delivers highly consistent results

3- And if a strong association is established between #1 and #2

Then the user can reliably count on his/her collimation tools and trust that star collimation will agree

 

Mike noted that based on his experience, he always found that star collimation detected/corrected small residual collimation errors even after using quality collimation tools on quality scopes. I do not have an answer for him.

 

I do not see star collimation being a regular part of my observation ritual. 

 

Jason


Edited by Jason D, 07 March 2015 - 11:47 AM.


#81 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 43270
  • Joined: 23 Jun 2003

Posted 07 March 2015 - 11:42 AM

Jason,

I could be wrong, but I don't think he uses Catseye tools, especially the autocollimator.

He did say he didn't have a good cheshire.

 

When I follow up the Glatter laser tools with a Catseye AC, I always find residual errors.

It seems that Mike may be using a star to do the same thing.



#82 MrJones

MrJones

    Vanguard

  • *****
  • Posts: 2462
  • Joined: 15 Sep 2010

Posted 07 March 2015 - 11:54 AM

Thanks everyone and especially Mike Lockwood for an informative thread.

 

I almost always tweak my Z12 collimation by star testing. Maybe it's all the SCT experience but I don't find it hard or time consuming at all.



#83 Nils Olof Carlin

Nils Olof Carlin

    Vanguard

  • *****
  • In Memoriam
  • Posts: 2227
  • Joined: 26 Jul 2004

Posted 07 March 2015 - 12:06 PM

....
 
Diameter of a much smaller, mostly coma-free spot = D/3 = 4.8mm ÷ 3 = 1.6mm
 
Radius of this much smaller, mostly coma-free spot = D/6 = 4.8mm ÷ 6 = 0.8mm at the level of the focal plane.
 
Tolerance of PAE as seen in the Cheshire photos = 2 x 0.8mm = 1.6mm
 
I recognize that this 1.6mm tolerance equates to D/3.


Most of my ideas in the first version of my collimation FAQ (-97) have caught on. But the engineering concepts of setting an acceptable tolerance, then using tools to ensure that these tolerances are met, have not become as widely accepted.
If the face of the Cheshire is near the focal plane, its reflection and the primary's center spot will appear the same scale.
So you can make a center spot that is 3.2 mm smaller than the face of the Cheshire.
Then, as long as you see the spot fully within the reflected bright face of the Cheshire, you know that you are within your tolerance. You might do better, of course, but the improvement is small to insignificant.

Nils Olof

#84 Kipper-Feet

Kipper-Feet

    Viking 1

  • *****
  • Posts: 680
  • Joined: 22 Jan 2014

Posted 07 March 2015 - 12:43 PM

 

....
 
Diameter of a much smaller, mostly coma-free spot = D/3 = 4.8mm ÷ 3 = 1.6mm
 
Radius of this much smaller, mostly coma-free spot = D/6 = 4.8mm ÷ 6 = 0.8mm at the level of the focal plane.
 
Tolerance of PAE as seen in the Cheshire photos = 2 x 0.8mm = 1.6mm
 
I recognize that this 1.6mm tolerance equates to D/3.


Most of my ideas in the first version of my collimation FAQ (-97) have caught on. But the engineering concepts of setting an acceptable tolerance, then using tools to ensure that these tolerances are met, have not become as widely accepted.
If the face of the Cheshire is near the focal plane, its reflection and the primary's center spot will appear the same scale.
So you can make a center spot that is 3.2 mm smaller than the face of the Cheshire.
Then, as long as you see the spot fully within the reflected bright face of the Cheshire, you know that you are within your tolerance. You might do better, of course, but the improvement is small to insignificant.

Nils Olof

 

 

 

Since you do not criticize or correct my numbers, which I had hoped form, I am going to assume that I am still on track with your way of doing things.  I gather then that my understanding of your D/4 and D/6 tolerances for the PAE is correct.  Yeah!

 

As for the rest, are you talking about a "graduated Cheshire"?

 

I imagine that a centre-spot that is 3.2mm smaller in diameter than the face of the Cheshire will also be 1.6mm smaller in radius than the face of the Cheshire.  

 

As such, when superimposed in the reflection in the mirrors, the small annular ring between them would have a width of 1.6mm.   This width would then be equivalent to the D/6 tolerance as seen above.

 

Since this is my first contemplation of such, is this what you mean?



#85 Nils Olof Carlin

Nils Olof Carlin

    Vanguard

  • *****
  • In Memoriam
  • Posts: 2227
  • Joined: 26 Jul 2004

Posted 07 March 2015 - 12:46 PM

Jason,
I could be wrong, but I don't think he uses Catseye tools, especially the autocollimator.
He did say he didn't have a good cheshire.
 
When I follow up the Glatter laser tools with a Catseye AC, I always find residual errors.
It seems that Mike may be using a star to do the same thing.


If instead you follow up with just the Blackcat, what do you find?

The limitation of the AC is that it is pretty useless for collimating the primary! (it may be a bit better in showing the focuser axis collimation, but not really that great).
The combination Blackcat and Hotspot are, I believe, the best commercial Cheshire-type tools available.
But unlike this, there is nothing you can see in the AC spot pattern that shows you the state of the primary's collimation.
Not even with the excentric pupil - if you see the P and 2 reflections coincide, this does not mean the primary is collimated (it only means the PAE and FAE are equal and opposite, not that they are zero).
(At http://web.telia.com...Acoll/Acoll.htm ), near the end, is a matrix of images borrowed from Jason that shows this - see in particular the second row of images).

Dixi et salvavi animam meam

Nils Olof

#86 Nils Olof Carlin

Nils Olof Carlin

    Vanguard

  • *****
  • In Memoriam
  • Posts: 2227
  • Joined: 26 Jul 2004

Posted 07 March 2015 - 01:53 PM

Since you do not criticize or correct my numbers, which I had hoped form, I am going to assume that I am still on track with your way of doing things.  I gather then that my understanding of your D/4 and D/6 tolerances for the PAE is correct.  Yeah!
 
As for the rest, are you talking about a "graduated Cheshire"?
 
I imagine that a centre-spot that is 3.2mm smaller in diameter than the face of the Cheshire will also be 1.6mm smaller in radius than the face of the Cheshire.  
 
As such, when superimposed in the reflection in the mirrors, the small annular ring between them would have a width of 1.6mm.   This width would then be equivalent to the D/6 tolerance as seen above.
 
Since this is my first contemplation of such, is this what you mean?


I take it you are fully competent with basic arithmetic - I saw no errors.
I mean the spot size is "graduated" with respect to the Cheshire size and telescope f/ratio.

This thing is not really necessary for routine collimation, but it is a good laboratory exercise.

Nils Olof

#87 Jason D

Jason D

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 7397
  • Joined: 21 Oct 2006

Posted 07 March 2015 - 02:14 PM

The limitation of the AC is that it is pretty useless for collimating the primary! (it may be a bit better in showing the focuser axis collimation, but not really that great).
The combination Blackcat and Hotspot are, I believe, the best commercial Cheshire-type tools available.
But unlike this, there is nothing you can see in the AC spot pattern that shows you the state of the primary's collimation.
Not even with the excentric pupil - if you see the P and 2 reflections coincide, this does not mean the primary is collimated (it only means the PAE and FAE are equal and opposite, not that they are zero).

 

I use XLKP-C AC it is equivalent to (XLKP AC + Blackcat) combo but it takes more skills to use XLKP-C AC. The photo below shows XLK-C. I upgraded it to XLKP-C last year.

Jason

 

5685847-XLK_C.jpg


#88 Kipper-Feet

Kipper-Feet

    Viking 1

  • *****
  • Posts: 680
  • Joined: 22 Jan 2014

Posted 07 March 2015 - 02:26 PM

Yes thank you Nils Olof, as a former structural engineer, I am competent with arithmetic and just a little bit of mathematics after that.

 

However, when it comes to learning this telescope stuff from the masters, I presume nothing.  I just investigate and then take from it what I can use.

 

Clearly, I do not always read the way that you write.  I don't mind appearing silly, however, in my subsequent efforts to learn what it is that you are offering even if it has not caught on in the rest of the amateur astronomy world.  

 

Without students, teachers have no purpose.  Please enjoy the fact that I want to learn what it is that you teach.

 

Thanks for help thus far.



#89 Jason D

Jason D

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 7397
  • Joined: 21 Oct 2006

Posted 07 March 2015 - 02:30 PM

Thanks everyone and especially Mike Lockwood for an informative thread.

 

I almost always tweak my Z12 collimation by star testing. Maybe it's all the SCT experience but I don't find it hard or time consuming at all.

 

The point of this thread is not to enforce what is considered a common practice of using star test to tweak collimation. The point of this thread is to challenge the notion that practical star collimation is accurate. To be clear, I am not challenging the accuracy of  theoretical star collimation but rather I am challenging the accuracy of practical star collimation. Anyone who asserts that his/her method of star collimation is more accurate might want to conduct similar experiments to what I have shown in this thread. For those who are knowledgeable about star collimation and are capable of achieve excellent consistency can make the accuracy claim. For those who can't achieve good consistency with star collimation should not make such a claim.

 

Jason



#90 Nils Olof Carlin

Nils Olof Carlin

    Vanguard

  • *****
  • In Memoriam
  • Posts: 2227
  • Joined: 26 Jul 2004

Posted 07 March 2015 - 02:52 PM

I use XLKP-C AC it is equivalent to (XLKP AC + Blackcat) combo but it takes more skills to use XLKP-C AC. The photo below shows XLK-C. I upgraded it to XLKP-C last year.
Jason


First, let me make it very clear that Jason is the sole innovator behind the "HotSpot", the eccentric extra pupil, and those extra rings at the edge, making it a "-C" model.
All of these are needed to make the AC on its own useful in practice (it wasn't, before Jason did his work)
Too bad the "-C" model isn't for sale yet - or am I wrong here?? Lacking it, the Blackcat + HotSpot is about the best you could use for instrument collimation of the primary.

Nils Olof

#91 Vic Menard

Vic Menard

    Fly Me to the Moon

  • *****
  • Posts: 6952
  • Joined: 21 Jul 2004

Posted 07 March 2015 - 03:13 PM

 

"Perfect collimation" is a pipe dream, but e.g. to judge the acceptable deviation as seen in Jason's images, you may set the tolerances to perhaps 1/2 or 1/3 of the tabulated radii (1/4 to 1/6 of the diameters).

 

...I understand that your Table refers to the diameter D of the sweet-spot at the level of the focal plane.

 

You suggest that it would be 'safer' to use a 'smaller' spot in which the coma would be 'lower'.

 

The reduced diameter of this 'smaller' spot could be made to be either D/2 or D/3.

 

The radii of these 'smaller' spots would then be D/4 or D/6 respectfully...

 

Richard, 

I don't think anyone is questioning your math.

But I still don't think you're fully understanding what Nils Olof is trying to explain with the primary mirror axial tolerance.

 

First, there is no smaller "sweet spot"--the sweet spot, or coma "free" field diameter is the area surrounding the primary mirror axis where coma will reduce the Strehl ratio by no more than 0.2. This coma "free" field diameter should be centered relative to the field stop of the eyepiece in the focuser.

 

This means if your high magnification eyepiece has a 5mm field stop, the central 4.75mm (using Everhart for the "sweet spot" diameter and an f/6 primary mirror) will be "diffraction limited" (assuming you're not using a coma corrector). That's almost the entire field of view!

 

Similarly, if you collimate your primary mirror and end up leaving a residual primary mirror error that's 1/2 of the coma "free" field diameter, the sweet spot will no longer be centered in the field stop but will instead be shifted about 2.4mm away from the center (in some direction). This means your best corrected area in the field of view will be somewhere along the edge (not good) and the center of the field of view will be reduced by 0.2 Strehl (your "perfect" primary and secondary mirrors' wavefront has just been reduced to 1/4 wave). This is why 1/4 of the coma free field diameter as an error tolerance is "better" and 1/6 may be important for achieving maximum resolution/detail when viewing planets or the Moon. 

 

Some will argue that the gains in image performance are unlikely to be noticed visually. (They'll rationalize their argument with claims of poor seeing, economy optics, no time to let their scope cool, and a host of other complaints.) You'll notice in Jason's signature his XT10 Classic has premium optics. For observers who "push the envelope" by upgrading their optics (not an "inexpensive" proposition), gratuitously losing any part of that performance gain is not negotiable...


Edited by Vic Menard, 07 March 2015 - 03:19 PM.


#92 Nils Olof Carlin

Nils Olof Carlin

    Vanguard

  • *****
  • In Memoriam
  • Posts: 2227
  • Joined: 26 Jul 2004

Posted 07 March 2015 - 03:15 PM

Thanks everyone and especially Mike Lockwood for an informative thread.
 
I almost always tweak my Z12 collimation by star testing. Maybe it's all the SCT experience but I don't find it hard or time consuming at all.


If you don't find it hard or time consuming at all, one wonders how accurately you succeed in doing it in practice. Do you get consistent indication of some error when you check with a known accurate method of instrument collimation of the primary (the gist of Jason's comment)?.


 

The point of this thread is not to enforce what is considered a common practice of using star test to tweak collimation. The point of this thread is to challenge the notion that practical star collimation is accurate. To be clear, I am not challenging the accuracy of  theoretical star collimation but rather I am challenging the accuracy of practical star collimation. Anyone who asserts that his/her method of star collimation is more accurate might want to conduct similar experiments to what I have shown in this thread. For those who are knowledgeable about star collimation and are capable of achieve excellent consistency can make the accuracy claim. For those who can't achieve good consistency with star collimation should not make such a claim.
 
Jason


I am glad to see the results of your experiment - I have long hoped for something like it, but I am not surprised by your results.
But one important aspect is you check your star collimating results using what I see as the golden standard of instrument collimation of the *primary* exclusively (namely the BlackCat in your case).
I would have more confidence in the reports of others, if they hade done so, too.

Nils Olof

Edited by Nils Olof Carlin, 07 March 2015 - 03:21 PM.


#93 Jason D

Jason D

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 7397
  • Joined: 21 Oct 2006

Posted 07 March 2015 - 03:42 PM

 

I use XLKP-C AC it is equivalent to (XLKP AC + Blackcat) combo but it takes more skills to use XLKP-C AC. The photo below shows XLK-C. I upgraded it to XLKP-C last year.
Jason


First, let me make it very clear that Jason is the sole innovator behind the "HotSpot", the eccentric extra pupil, and those extra rings at the edge, making it a "-C" model.
All of these are needed to make the AC on its own useful in practice (it wasn't, before Jason did his work)
Too bad the "-C" model isn't for sale yet - or am I wrong here?? Lacking it, the Blackcat + HotSpot is about the best you could use for instrument collimation of the primary.

Nils Olof

 

 

That you for the kind words, Nils Olof,

My AC contribution is a continuation to what I have learned from your AC research. My collimation knowledge was built on all the information I gained from you and Vic.

My understanding is that Jim Fly will sell the "-C" if requested. But as I have mentioned it is little more challenging to use compared to "XLKP/Blackcat" combo. Personally, I have mastered the art of using it. With the "-C" model, I do not even use the central pupil. I completed extensive work on comparing XLKP-C to XLKP/Blackcat and there is no doubt they are equivalent. I might even argue that the XLKP-C has a slight edge over the combo since it does not have any kind of parallax errors. I need to be careful here. I am not encouraging anyone who already owns XLKP/Blackcat combo to upgrade to XLKP-C.

Jason



#94 Jason D

Jason D

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 7397
  • Joined: 21 Oct 2006

Posted 07 March 2015 - 03:46 PM

 

I would have more confidence in the reports of others, if they hade done so, too.

 

 

I also would love to see results from others. In fact, I would like to encourage as many readers of this thread as possible to do the same experiment then uploaded their photos + analysis + opinion in this thread. I used my iphone 5s to take the photos. No special bracket -- just handheld iphone 5s.

 

Jason



#95 Vic Menard

Vic Menard

    Fly Me to the Moon

  • *****
  • Posts: 6952
  • Joined: 21 Jul 2004

Posted 07 March 2015 - 04:11 PM

First, let me make it very clear that Jason is the sole innovator behind the "HotSpot", the eccentric extra pupil, and those extra rings at the edge, making it a "-C" model.

All of these are needed to make the AC on its own useful in practice (it wasn't, before Jason did his work)
Too bad the "-C" model isn't for sale yet - or am I wrong here?? Lacking it, the Blackcat + HotSpot is about the best you could use for instrument collimation of the primary.

 

I think you're remiss in failing to mention the advent of the 2-inch autocollimator (with its wider field of view, better first surface mirror, and improved build quality), smaller pupil(s), deeper barrels for better registration, and most recently, precision etched pupil(s)--all innovations that were provided by Jim Fly of CatsEye Collimation. Collimation innovation is being driven today by manufacturers like Jim Fly ("passive" tools) and Howie Glatter (lasers and accessories).

 

I like the HotSpot for alignments utilizing my CatsEye tools, but I prefer the triangular CatsEye center spot when using my 1mm aperture stopped Glatter laser. Jim has even made a customized HotSpot for my evaluation with the Glatter laser. 

 

Many years ago, when Tectron Telescopes was the innovator of 1.25-inch collimation tools, the primary mirror center spot was a small square that showed the optimal primary mirror alignment by the visibility of the square's corners equally protruding from the Cheshire perforation. I would guess the error read precision was somewhere around +/-0.02-inch, maybe a little better, and it worked well in daylight and after dark.

 

Even so, we've come a long way, thanks in part from innovators like Jim and Howie, and people like you and Jason who were relentless in fine tuning Newtonian collimation theory and practice. And I got my wish that I expressed on another online forum some ten plus years ago, that eventually we would see a kind of "grand unified theory" of collimation. That, is an accomplishment in which I was fortunate to be able to play a small part, and for that you will have my endless thanks.   :bow:


Edited by Vic Menard, 07 March 2015 - 04:51 PM.


#96 catboat

catboat

    Surveyor 1

  • *****
  • Posts: 1653
  • Joined: 01 Dec 2009

Posted 07 March 2015 - 05:57 PM

 

Many years ago, when Tectron Telescopes was the innovator of 1.25-inch collimation tools, the primary mirror center spot was a small square that showed the optimal primary mirror alignment by the visibility of the square's corners equally protruding from the Cheshire perforation. I would guess the error read precision was somewhere around +/-0.02-inch, maybe a little better, and it worked well in daylight and after dark.

 

 

 

Vic,  I’m still using those Tectron tools (also have the Glatter gear).  Maybe I can ask a question here about the using the Tectron autocollimator.  The problem is that on my 6” with a small white donut center spot, I can’t see a thing through the autocollimator.  Well, maybe a I can if pointed at well-lit window, but it’s a strain and uncertain.  Most of the time I can’t make out the reflections at all.  

 

Someday I’ll get the 2” Catseye autocollimator, but in the meantime is there anything to be done?  A different type of center marker?  A different technique to see the reflections better? 



#97 backwoody

backwoody

    Surveyor 1

  • -----
  • Posts: 1713
  • Joined: 08 Jan 2007

Posted 07 March 2015 - 06:15 PM

Hi Catboat, I'm a Tectron user too...and consistently get excellent results with those 1.25" tools.  Using the Tectron AC, I find it's best to actually use a very well-lit situation, regardless of which type of centermark is on your primary. My favorite scenario is to get the scope into position well before dark, collimate as necessary in daylight (including with the AC), and then wait for darkness as the mirror cools.  I do not find it necessary to re-collimate during viewing, and in fact, generally find almost no adjustments are needed the next day.

 

I am planning to upgrade to a Catseye AC, however, to take advantage of all the advances achieved by the gentlemen who have contributed to this post.

 

And to Vic, Nils Olof, Jason, and Don, thank you for another exceptionally educational thread.

 

Salut.



#98 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 43270
  • Joined: 23 Jun 2003

Posted 07 March 2015 - 06:18 PM

Yes, point the scope at a bright daytime sky and get as much light into the tube as possible.

I even find the reflections easier to see if I point near the sun, where the sky is brightest.

Be careful you don't point AT the sun, however.

If it's am, point BELOW the sun.  If it's pm, point ABOVE the sun.  That way, direct sunlight will never enter the scope.

Once the field is adequately illuminated, you will see the reflections.  I used to use a Tectron autocollimator and never had an issue seeing all the reflections

in my 6" f/5 of the time as long as I used the daytime sky as the light provider.



#99 catboat

catboat

    Surveyor 1

  • *****
  • Posts: 1653
  • Joined: 01 Dec 2009

Posted 07 March 2015 - 06:29 PM

Thank you, Woody and Don!  I’ll get more daylight into the tube and keep at it.



#100 Brian Carter

Brian Carter

    Fly Me to the Moon

  • *****
  • Posts: 5044
  • Joined: 24 Nov 2004

Posted 07 March 2015 - 08:21 PM

In the evening, a bright led light aimed at the mirror works in a pinch. Do it before you're dark adapted though.


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics